Among benzoyl compounds, those which are known as compounds having benzophenone in the structure include: Compound A having anti-tumor activity (WO01/81288); Compound B referred to as HMP-M4 (J. Antibiotics, 2002, Vol. 55, p. 61-70); Compound C (J. Am. Chem. Soc., 1971, Vol. 93, p. 6708-6709); Compound D having eosinophilic leukocyte function inhibiting activity (Japanese Published Unexamined Patent Application No. 92082/1996; Bioorg. & Med. Chem. Lett., 1999, Vol. 9, p. 1945-1948); Compound E (Tetrahedron Lett., 2002, Vol. 43, p. 291-293); and Compound F (J. Chem. Soc., Perkin Trans. 1, 1989, p. 441-448). Further, compounds having benzophenone in the structure and methods for synthesis of the compounds are known [e.g. Japanese Published Unexamined Patent Application No. 39968/2001; U.S. Pat. No. 6,125,007; J. Chem. Soc., Perkin Trans. 1, 1977, p. 2502-2512; J. Chem. Soc., Perkin Trans. 1, 1974, p. 1417-1421; J. Chem. Soc. (C), 1971, p. 3899-3902; Tetrahedron Lett., 1981, Vol. 22, p. 267-270].

Benzoquinone ansamycin antibiotics such as Geldanamycin and Herbimycin, and Radicicol are known as compounds which bind to heat shock protein 90 (Hsp90) family proteins (Cell Stress & Chaperones, 1998, Vol., 3, p. 100-108; J. Med. Chem., 1999, Vol., 42, p. 260-266). These compounds are all reported to bind to Hsp90 family proteins and inhibit the functions of Hsp90 family proteins, thereby exhibiting pharmacological activities such as anti-tumor activity. Therefore, compounds binding to Hsp90 family proteins are considered to be useful as therapeutic agents for diseases associated with Hsp90 family proteins or proteins to which Hsp90 family proteins bind (Hsp90 client proteins).
Examples of known Hsp90 family proteins include Hsp90α protein, Hsp90β protein, grp94 and hsp75/TRAP1 (Pharmacology & Therapeutics, 1998, Vol., 79, p. 129-168; Molecular Endocrinology, 1999, Vol., 13, p. 1435-1448; etc.).